PB0575 - Novel Variants of PROS1 Gene Related to Protein S Deficiency

Background: Plasma Protein S (PS) exists in a free and bound form. Free PS functions as an anticoagulant by directly inhibiting Factor IXa, thereby limiting thrombin generation. Protein S deficiency increases the risks of life-threatening venous thromboembolism and disseminated intravascular coagulation. Protein S deficiency is an inherited autosomal dominant condition with variable penetrance.

Aims: To assess genetic and protein data related to Protein S deficiency.

Methods: Plasma assays: activated partial thromboplastin time (aPTT), thrombin generation assay (TGA), immunoblotting, and enzyme linked immunosorbent assays (ELISA). The PROS1 gene was sequenced from whole blood of two control samples and the patient samples.

Results: Immunoblotting revealed an 18% decrease in total PS and ELISA revealed a 46% decrease in free PS in patient 1. Patient 2 also had significant decreases in total and free PS. Functional tests (aPTT and TGA) showed decreased clotting time and increased thrombin generation, which indicated that the patients have reduced levels of PS. There were five variations in patient 1’s PROS1 gene, three of which are novel variations. Variant c.1061+62_1061+63insA in intron 10 was found in both subjects . This insertion may create a donor site according to SSF, MaxEnt, and NNSPLICE predictors. Donor site alteration may cause skipping of exon 10 and partial intron retention. Variant c.945+93del is in intron 9 and may produce a new cryptic acceptor site. Variant, c.443-159del, is in intron 5 and may produce two new cryptic acceptor splice sites. Both changes can produce an isoform of PS or a nonfunctional protein, possibilities that require experimental confirmation.

Conclusion(s): Both individuals had reduced levels of PS and the same novel variant in intron 10 of PROS1. Future research should examine the patients’ family histories and assess family members for genetic variations in PROS1.